A conventional internal intermediate pressure type multistage rotary compressor of this type is, for example, disclosed in Japanese Laid-Open Publication No. 2-294587 (F04C23/00). Such a rotary compressor is provided with an electric element in a hermetic shell case and a rotary compression mechanism which is positioned under the electric element and comprises first and second rotary compression elements which are driven by a rotary shaft of the electric element. When the electric element is actuated to rotate the rotary shaft, refrigerant is sucked into a low pressure chamber of a cylinder through a suction port of the first rotary compression element (first stage) provided under the electric element, and the refrigerant is subjected to compression of first stage by the operation of the roller and a vane and is changed into intermediate pressure refrigerant, which is in turn discharged from a high pressure chamber of a cylinder into the hermetic shell case under the electric element through a discharge port, a noise eliminating chamber, and an intermediate discharge pipe.
Oil is separated from the intermediate pressure refrigerant discharged into the hermetic shell case, and the refrigerant flows into a refrigerant introduction pipe provided under the electric element, and passes through the outside of the electric element, then is sucked into the low pressure chamber of a cylinder 238 through a suction port 261 of the second rotary compression element 234 (second stage) as shown in the left side of FIG. 22, wherein it is subjected to compression of second stage by the operation of the roller 246 and the vane 250, which is in turn changed into high temperature high pressure refrigerant. The high temperature high pressure refrigerant passes through a discharge port 239, a noise eliminating chamber, and is discharged into a refrigeration circuit through the outside of the refrigerant discharge pipe. A cycle of the thus discharged refrigerant is repeated such that the discharged refrigerant flows into a radiator (gas cooler) and the like of the refrigeration circuit, and radiates heats, then it is throttled by an expansion valve and heat thereof is absorbed by an evaporator, and it returns to the first rotary compression element through the refrigerant introduction pipe and is sucked in the first rotary compression element.
In this case, displacement of the second rotary compression element is normally set to be smaller than that of the first rotary compression element.
An oil path is provided in the rotary shaft of such a rotary compressor, and oil stored in the oil reservoir provided at the bottom of the hermetic shell case is pumped up in the oil path by an oil pump (supply means) attached to the lower end of the rotary shaft. The thus pumped up oil is supplied to the rotary shaft and the sliding portions and bearings of the first and second rotary compression elements so as to lubricate therein and seal them, and it is discharged through an oil discharge port provided at the upper end of the rotary shaft so as to cool the electric element in the hermetic shell case and lubricate various sliding portions at the periphery thereof.
In the internal intermediate pressure multistage compression type rotary compressor, the refrigerant compressed by the second rotary compression element is discharged outside as it is. However, the foregoing oil which is supplied to the sliding portions of the second rotary compression element is mixed in the refrigerant, and hence the oil is discharged together with the refrigerant. Accordingly, there arises a problem that a large amount of oil flows in refrigeration circuit of the refrigerating cycle, thereby deteriorating the performance of refrigerating cycle.
Further, with such a rotary compressor, since a pressure (high pressure) in the cylinder of the second rotary compression element is higher than a pressure (intermediate pressure) in the hermetic shell case having the bottom serving as the oil reservoir, it is difficult to supply oil to the second rotary compression element utilizing the difference in these pressures.
Therefore, it is contemplated that the intermediate pressure refrigerant discharged from the first rotary compression element is not discharged into the hermetic shell case, but the high pressure refrigerant discharged from the second rotary compression element is discharged into the hermetic shell case, thereby rendering the interior of the hermetic shell case to be high pressurized. That is, with such an internal high pressure multistage compression type rotary compressor, the refrigerant is sucked through the suction port of the first rotary compression element in the low pressure chamber of the cylinder, and it is subjected to compression by the operation of the roller and the vane and is changed into the intermediate pressure, which is in turn discharged from the high pressure chamber of the cylinder into the discharge port and the noise eliminating chamber. The refrigerant discharged into the noise eliminating chamber passes through the refrigerant introduction pipe, and it is sucked in the low pressure chamber of the cylinder through the suction port of the second rotary compression element, then it is subjected to compression of second stage by the operation of the roller and vane and is changed into a high temperature high pressure refrigerant, which is in turn discharged from the high pressure chamber into the hermetic shell case through the suction port and the noise eliminating chamber.
Although it is configured that the high pressure refrigerant in the hermetic shell case flows into a radiator through the refrigerant discharge pipe, it is expected that the amount of oil to flow outside can be reduced and the supply of oil to the sliding portions can be easily performed.
With such a multistage compression type rotary compressor, when the refrigerant introduction pipe relative to the second rotary compression element is opened to the space under the electric element, the distance between the first rotary compression element and the intermediate discharge pipe for discharging the refrigerant is short so that oil is not sufficiently separated from the refrigerant, and hence excessive oil is sucked in the second rotary compression element. In such a case, since the amount of oil which is discharged from the second rotary compression element into an external refrigeration circuit through the refrigerant discharge pipe becomes large, the lubricating and sealing performance in the hermetic shell case of the rotary compressor is deteriorated, causing a problem of an adverse affect in the refrigeration circuit by the oil.
If the refrigerant introduction pipe relative to the second rotary compression element is opened to the space over the electric element to solve the foregoing problem, there arises another problem that a height dimension of the compressor is enlarged as a whole. Further, there arises still another problem that the oil discharged from the upper end of the rotary shaft is prone to flow into the refrigerant introduction pipe, to induce inconvenience like the foregoing problems.